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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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  1.  
    Posted By: GreenPaddy You could add a remote humidistat to the existing fan, maybe something like this...
    https://crwltd.co.uk/extractor-fan-inline-bathroom-run-on-timer--humidity-sensor-switch-socket-2335-p.asp?


    Fantastic! - I will explore this avenue.
  2.  
    Posted By: GreenPaddy What is it you're trying to control? RH in the bathroom, at the window...You might want to be able to de-activated it so it can't come on at night, as say room temp falls, and RH rises. I think I might just put a timer on it, and be done with it. Increase the time period if you see a bit more cond. Off between 10pm and 7am, or what ever.


    The minimum is to prevent condensation in the main room where the bifold cill meets the wooden floor. This is about 12m away from the extractor fan at the opposite end of the barn.
  3.  
    Posted By: GreenPaddy That doesn't really help with the main thrust of your question - how to not repeat this in the house.


    Now I know the condensation is just caused by people occupying the barn, I can be confident that the new house will be fine with MVHR and the same windows (and see below).
  4.  
    Posted By: GreenPaddy As others have said, you have a cold bridge at the foot of the window. It may be resting on the metal cill, and bridging the cavity. So metal cill from inside to out, and possibly cold air directly underneath from cavity. Is the cill thermally broken? Is the unit sitting on insulation? Door thresholds and floor based window cill details are often a problem.


    Bifold frame sits on 36mm plywood packers on top of concrete blocks. It didn't occur to me that I might be creating a cold bridge by doing so. The plywood supports both front and back of the cill so bridges the thermal break. Arghh.

    Well at least I know what not to do in the main house!. I think I might have thought that plywood wasn't enough of a thermal conductor to matter very much.
      bifold cill.png
    • CommentAuthordickster
    • CommentTimeJan 8th 2021
     
    Hope it's marine ply!
    • CommentAuthorborpin
    • CommentTimeJan 8th 2021
     
    Re AC/h and m³/h/m² my point was that 1.7 AC/h is very likely to be different to 1.7 m³/h/m² (or m/h).
  5.  
    For when we get to building the new house I need to know what insulation to put under the cills. I've had a look at some previous discussions on GBF. We will be having sliding doors 2300mm high. Not sure yet if they'll be double or triple glazed.

    Is Compacfoam 200 still the go-to solution?
    •  
      CommentAuthordjh
    • CommentTimeJan 8th 2021
     
    Posted By: chrisduncanFor when we get to building the new house I need to know what insulation to put under the cills. I've had a look at some previous discussions on GBF. We will be having sliding doors 2300mm high. Not sure yet if they'll be double or triple glazed.

    Is Compacfoam 200 still the go-to solution?

    You need to know the weight of the doors and the stated pressure limit of whatever you put underneath, plus any requirements the door manufacturers make for flatness and rigidity (if they require something flatter than whatever you put under it compresses by at working load, you might need something stiffer).

    As far as I'm aware Compacfoam is still good stuff. It comes in various stiffnesses, not just 200.
  6.  
    In the diagram, what is the dashed line that starts beneath the rollers and ends beneath the tip of the cill with a water droplet symbol?

    Is that an air leakage path as well as a drainage path?
    •  
      CommentAuthordjh
    • CommentTimeJan 8th 2021
     
    Posted By: WillInAberdeenIs that an air leakage path as well as a drainage path?

    Isn't any drainage path automatically (a fortiori) an air leakage path?

    I think the only air seal is inboard,where the sealant is shown to be applied and there's a flexible seal shown above mating against the bottom of the door.
  7.  
    Have you carried out work for the renovation which is prehaps now drying out/releasing water vapour?
    • CommentAuthorlineweight
    • CommentTime4 days ago edited
     
    Interesting to read through this thread and to see the finger ending up pointing at the bifold sill detail!

    I'm always worrying about the detail under bifolds and in my experience the suppliers/manufacturers are entirely unhelpful in offering any advice on details that avoid a thermal bridge at this location.

    In particular, the question of bridging a cavity in a situation where you are building into a cavity wall type buildup. A while back I spent ages trying to find whether there was such thing as a load-bearing cavity closer for this type of situation. My conclusion - there isn't.

    http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16054
  8.  
    As an aside - the basic problem with dealing with this sill/threshold situation is that the bifold systems generally demand a flat continuous surface for the entirety of the sill to sit on. And the sills are often very deep when you have several tracks and triple glazing - often the same or greater than the thickness of the whole wall buildup.

    So, if you have an insulated cavity, you have to have something that can bridge it structurally. And the materials that can do that tend to have bad insulation values.

    But the sill is thermally broken (as per the diagram posted above)... and I might be wrong, but I imagine it is designed such that the load from the sliding tracks is not passed through the thermal break section - in other words, it must be shared by the aluminium bits either side. So potentially you don't actually need structural support directly under the thermal break section.

    So, can't it just be designed so that the thermal break in the frame sill can be aligned with the insulation layer in the wall below?

    Perhaps it's just not structurally feasible to have an aluminium sill element that can bridge a 100mm or so cavity.
    • CommentAuthorlineweight
    • CommentTime4 days ago edited
     
    Posted By: chrisduncan

    Bifold frame sits on 36mm plywood packers on top of concrete blocks. It didn't occur to me that I might be creating a cold bridge by doing so. The plywood supports both front and back of the cill so bridges the thermal break. Arghh.

    Well at least I know what not to do in the main house!. I think I might have thought that plywood wasn't enough of a thermal conductor to matter very much.
      http:///newforum/extensions/InlineImages/image.php?AttachmentID=7749" alt="bifold cill.png" >


    The thermal bridge is likely to be caused by the concrete block directly under the ply, rather than the ply itself no?

    In other words there is a path horizontally through the conc block, then once it gets to the inside, you're just relying on the thickness of the ply layer (rather than its depth outside-to-inside).
    •  
      CommentAuthordjh
    • CommentTime3 days ago
     
    Posted By: lineweightSo, can't it just be designed so that the thermal break in the frame sill can be aligned with the insulation layer in the wall below?

    I think the difficulty with that is:
    (a) the thermal break in the frame is actually quite narrow, so there's not much space for insulation, and it's clear in the drawing that the frame needs supporting adjacent to the thermal break, (aerogel maybe?) and
    (b) you then have the difficulty of making sure that the two separate structural parts are exactly level with each other and maintain that equality of level over time.

    Is one of the Compacfoam products stiff enough to be used underneath a bifold? Or Marmox Thermoblocks or Foamglas Perinsul? And are they strong enough (I guess so, though fixings might be problematic)

    When we built, bifolds were regarded as not suitable for PH, so we didn't consider them. I think there are now some PH-certified, so it might be worth asking them for installation details?
  9.  
    Yes I think you are right about the difficulties.

    (a) I was wondering whether there is a potential design of the frame that would allow a wider thermal break
    (b) Yes, I see that in principle, although you could argue this is an issue even if you bridge the leaves further down somehow.

    My understanding was that stuff like compacfoam is only strong in compression, not designed to span across gaps, but I might be wrong.

    Yes, perhaps I should look at PH bifolds, if such a thing exists. Things might have moved on in the year or two since I last looked at this.
    •  
      CommentAuthordjh
    • CommentTime3 days ago
     
    Posted By: lineweight(b) Yes, I see that in principle, although you could argue this is an issue even if you bridge the leaves further down somehow.

    It all depends on the foundation design. A passive slab with an outer wythe supported on separate strip foundations is probably going to be about the worst case, and a trenchfill foundation with two brick wythes on top is likely about the best case. Avoiding such issues is one advantage of not using cavity construction for me.

    My understanding was that stuff like compacfoam is only strong in compression, not designed to span across gaps, but I might be wrong.

    Once you've committed to putting it in, you can safely join the construction underneath, I expect. Depends on the exact details I suppose.

    perhaps I should look at PH bifolds, if such a thing exists

    A quick search for PH bifolds shows that they do exist. The Danish firm Lacuna looks interesting. What they say is that their doors are top-hung. I expect that gets around most of the problem, since the bottom guide rail won't carry much load.
    • CommentAuthorLF
    • CommentTime3 days ago
     
    Insulators - strong - may be of use ?


    permali glass was used in cryogenic plant design and was really tough stuff.
    google says - https://permalideho.co.uk/products/

    We used like in these photos
    https://www.rilco.com/products/isolation-blocks-additional-components


    Sindanyo block was another similar one.

    I was only doing heat leak calcs not mechanical and it was nearly 30 years ago.
  10.  
    DJH - yes, in some situations you can join the construction underneath where you'd put the compacfoam layer and I think that can work fine at a ground floor detail where you can line the compacfoam up with the floor insulation but it doesn't work if you're at an upper level and you need the insulation layer to carry on downwards uninterrupted.

    Although this does kind of highlight a disadvantage of cavity construction, yes, it does still sort of exist with other buildups too, because you do inevitably have to bridge the insulation layer with something that's strong enough to walk on.

    As I understand it, unfortunately top hung bifolds are usually more expensive partly because you have to provide the suitable structure at high level.

    It might just be that if you want to have bifolds and also do things properly, it's not cheap.

    (Actually when I said bifolds, I really meant sliders, because sliders tend to have several tracks in parallel and this means you can end up with very deep sills to accommodate)
    • CommentAuthorlineweight
    • CommentTime3 days ago edited
     
    Posted By: LFInsulators - strong - may be of use ?


    permali glass was used in cryogenic plant design and was really tough stuff.
    google says - https://permalideho.co.uk/products/

    We used like in these photos
    https://www.rilco.com/products/isolation-blocks-additional-components


    Sindanyo block was another similar one.

    I was only doing heat leak calcs not mechanical and it was nearly 30 years ago.


    Looks interesting but generally I'm looking for something that is specifically intended for the purpose - for confidence and cost reasons.
    • CommentAuthordickster
    • CommentTime3 days ago
     
    Wooden beam as support, a compromise?
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